This document relates to semiconductor devices including semiconductor photodetectors and photodetector arrays.
Semiconductor pn junctions can be used to construct photodiodes for detecting photons. An avalanche diode is one example of such photodiodes. Single-photon avalanche diodes (SPADs) are designed to detect single photons and can be used in a variety of applications, including biological, military and biometric applications. A SPAD can be operated in a Geiger mode to output a signal that represents a photon-arrival event or the time of arrival of a photon. As such, SPADs can be used as low-light-level imagers, sensors for Time-Correlated Single-Photon Counting and Fluorescence Correlation Spectroscopy and other sensing applications. When operated in the Geiger mode, a SPAD is in essence a reverse-biased pn junction which can sustain numerous avalanche breakdowns without incurring damage and with minimal charge trapping. When a photon is absorbed in the high-field region of the SPAD, the SPAD generates an electron-hole pair which can induce an avalanche through impact ionizations. This avalanche can be electrically sensed with high timing accuracy, and is quickly quenched. The pn junction is then reactivated by recharging the junction in excess of its breakdown voltage.